I work on Delphi 6 and try to make communication between 2 process with windows message. One of the process (Process1) is not a window so I use the MsgHandler to create an invisible windows. I create 2 handlers using AddMsgHandler and wait for messages from the other process (Process2).

Process2 send 2 different kinds of message, one is is a PostMessage with lparam containing an integer value (it works) but the second is a SendMessage with lparam containing TCopyDataStruct and here is the issue, Porcess1 never receive the messages.